after pulling master a minute ago i wasn't able to build pants until i blasted ~/.cache/pants -- is this intended?

X> ./pants -V
info: (Busing existing install for '1.20.0-x86_64-apple-darwin'
info: (Boverride toolchain for '/Users/dmcclanahan/tools/pants' set to '1.20.0-x86_64-apple-darwin'

  1.20.0-x86_64-apple-darwin unchanged(B - rustc 1.20.0 (f3d6973f4 2017-08-27)

generating /Users/dmcclanahan/tools/pants/src/rust/engine/src/cffi/native_engine.c
(already up-to-date)
generating /Users/dmcclanahan/tools/pants/src/rust/engine/src/cffi/native_engine.cflags
   Compiling grpcio-sys v0.1.1 (<https://github.com/illicitonion/grpc-rs?rev=2acabdbff71e77a14b95b0b30c6d7de516355df7#2acabdbf>)
   Compiling regex v0.2.2
   Compiling generic-array v0.8.3
error: failed to run custom build command for `grpcio-sys v0.1.1 (<https://github.com/illicitonion/grpc-rs?rev=2acabdbff71e77a14b95b0b30c6d7de516355df7#2acabdbf>)`
process didn't exit successfully: `/Users/dmcclanahan/tools/pants/src/rust/engine/target/release/build/grpcio-sys-8e3295ec4e146d45/build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'Can't find module grpc/third_party/zlib. You need to run `git submodule update --init --recursive` first to build the project.', /Users/dmcclanahan/.cache/pants/rust-toolchain/git/checkouts/grpc-rs-a357d41b20dd2a82/2acabdb/grpc-sys/build.rs:59:16
note: Run with `RUST_BACKTRACE=1` for a backtrace.